HVAC DESIGN CONSIDERATIONS

HVAC DESIGN CONSIDERATIONS
Engineer Fahad Hasan Yousuf Hasan Associates Consulting Engineers

HVAC Design Considerations
Good HVAC Design is something more than controlling temperature and humidity and following information mandatory before start of HVAC Design Use of space and occupancy The time of day in which greatest occupancy occurs Physical building characteristics Lighting and equipment details Engr. Fahad Hasan, Y.H.Associates,

Basic considerations Electric power – size of service Heating – availability of steam, hot water, gas, oil or electricity Cooling – availability of chilled water, well water, city water and water conservation equipment Internal heat gains Equipment locations Engr. Fahad Hasan, Y.H.Associates,

Structural Considerations Rigging and delivery of equipment Obstructions Ventilation – opening through roof or wall for outdoor air duct Exposed and envelop material details Orientation and shading information Code requirements Utility rates and regulations Building Standards Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SMALL STORES
Small stores are typically located in convenience centers and may have at least the store front exposed to outdoor weather. Large glass areas found at the front of many small stores may cause high peak solar heat gain unless they have northern exposures or large overhangs. High heat gain may be experienced in the front of these stores. The HVAC System for this portion of the small store should be designed to offset the greater cooling and heating requirements Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SMALL STORES DESIGN CONSIDERATIONS System Design
Single zone unitary rooftop equipment or ducted split units is common in store air conditioning. Using multiple units to condition the store involves less ductwork and can maintain comfort in the event of partial equipment failure. Controls Controls for small stores should be kept as simple as possible while still providing the required factions. Unitary equipment is typically available with manufacturer-supplied controls for easy installation and operation. Time clock control can limit unnecessary HVAC operation. Unoccupied reset controls should be provided in conjunction with timed control. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SMALL STORES DESIGN CONSIDERATIONS Air Distribution
External static pressure available in small store air-conditioning units are limited, and air distribution should be designed to keep duct resistance low. Duct velocities should not exceed 1200 fpm, and pressure drop should not exceed 0.10 in of water per 100 ft. Average air quantities, typically ranges from 350 to 450 cfm per ton of cooling in accordance with the calculated internal sensible heat load. The duct system should contain enough dampers for air balancing. Volume control dampers should be installed in takeoffs from the main supply duct to balance air to branch ducts. Damper should be installed in the return and outdoor air ducts for proper outdoor air /return air balance and for economize operation Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities DEPARTMENT STORES
Department stores vary in size, type and location, so air conditioning design should be specific to each store. Essential features of a quality system include An automatic control system properly designed to compensate for load fluctuations Zoned air distribution to maintain uniform conditions under shifting loads Use of outdoor air for cooling during favorable conditions. It is also desirable to adjust inside temperature for variations in outdoor temperature. Although close control of humidity is not necessary, a properly designed system should operate to maintain relative humidity of 50% or below. The humidity limit eliminate musty odors and retards perspiration,, particularly in fitting room. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities DEPARTMENT STORES LOAD DETERMINATION
Because the occupancy (except store staff) is transient, inside conditions are commonly set not to exceed 78 deg F dry bulb and 50% RH at outdoor summer design conditions and 70 deg F at outdoor winter design conditions. Winter humidification is seldom used in store air conditioning. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities DEPARTMENT STORES DESIGN CONSIDERATIONS
Before performing load calculations, the designer should examine the store arrangement to determine what will affect the load and the system design. For existing buildings, actual construction, floor arrangement and load sources can be surveyed. For new buildings, examination of the drawings and discussion with the architect or owner is required. Larger stores may contain food services areas, warehouse space, extensive office area etc. Some of these special areas may operate during hours in addition to normal store open hours. If present or future operation could be compromised by such a strategy, these spaces should be served by separate HVAC systems. Engr. Fahad Hasan, Y.H.Associates,

System Design Air conditioning systems for department stores may use unitary or central station equipment. Selection should be based on owing and operating costs as well as special considerations for the particular store, such as store hours, load variations and size of load. Large department stores have often used central-station systems consisting of air handling units having chilled water cooling coils, fans and filters. Air systems must have adequate zoning for varying loads, occupancy and usage. Water chilling plants distribute water to the various air handlers and zones and may take advantage of some load diversity throughout the building. Engr. Fahad Hasan, Y.H.Associates,

Air Distribution All buildings must be studied for orientation, wind exposure, construction and floor arrangement. These factors affect not only load calculations, but also zone arrangements and duct locations. In addition to entrances, wall areas with significant glass, roof areas, and population densities, the expected locations of various departments should be considered. Flexibility must be left in the duct design to allow for future movement of departments. It may be necessary to design separate air systems for entrances, particularly in northern areas. This is also true for storage areas where cooling is not contemplated. Air curtains may be installed at entrance doorways to limit infiltration of unconditioned air, at the same time providing greater ease of entry. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities DEPARTMENT STORES DESIGN CONSIDERATIONS Controls
Space temperature controls are usually operated by staff who have little knowledge of air conditioning. Therefore exposed sensors and controls should be kept as simple as possible while still providing the required functions. Controls must be such that correctly conditioned air is delivered to each zone. Outdoor air intake should be automatically controlled to operate at minimum cost while providing required air flow. Partial or full automatic control should be provided for cooling to compensate for load fluctuations. Time clock control can limit unnecessary HVAC operation. Unoccupied reset controls should be provided in conjuction with timed control. Automatic dampers should be placed in outdoor air inlets and in exhausts to prevent air entering when the fan is turned off. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities CONVENIENCE CENTERS
Many small stores, discount stores, supermarkets, drugstores, theaters, and even department stores are located in convenience centers. The space for an individual store is usually leased. Arrangements for installating air conditioning in leased space vary. Typically, the developer builds a shell structure and provides the tenant with an allowance for usual cooling and other minimum interiror finish work. The tenant must then install an HVAC system. In stores with the shell construction, often before the space is leased or the occupancy is known. Larger stores typically provide their own HVAC design and installation. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities CONVENIENCE CENTERS DESIGN CONSIDERATIONS
The Developer or owner may establish standards for typical cooling that may or may not be sufficient for the tenants specific requirements. The tenant may therefore have to install systems of different sizes and types than originally allowed for by the developer. The tenant must ascertain that power and other services will be available for the total intended requirements. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SHOPPING CENTERS
Shopping centers generally incorporate an enclosed air-conditioned mall. These centers are normally owned by a developer, who may be an independent party, a financial institution or one of the major tenants in the center. Some shopping centers are designed with an open pedestrian mall between rows of stores. This open-air concept results in tenant spaces similar to those in a convenience center. Storefronts and other perimeters of the tenant spaces are exposed to exteriror weeather condtions. Major department stores in shopping centers are tyically considered sperate buildings, although they are attached to the mall. The space for individual small stores is the individually leased spaces vary, but are similar to those for small stores in convenience centers. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SHOPPING CENTER DESIGN CONSIDERATIONS
The owner or developer provides the HVAC system for an enclosed mall. The regional shopping center may use a central plant or unitary equipment. The owner generally requires that the individual tenant stores connect to a central plant and includes charges for cooling services. Where unitary systems are used, the owner generally requires that the individual tenant install a unitary system of similar design. Owner may establish standards for typical cooling systems that may or may not be sufficient for the tenants specific requirements. Therefore, the tenant may have to install systems of different sizes then originally allowed for by the developer Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SHOPPING CENTER DESIGN CONSIDERATIONS
Leasing arrangements may include provisions that have a detrimental effect on conservation (such as allowing excessive lighting and outdoor air or deleting requirements for economizer systems). The designer of HVAC for tenants in a shopping center must be well aware of the lease requirements and work closely with leasing agents to guide these systems towards better energy efficiency. Many regional shopping centers contain specialty food court areas that require special considerations for odor control, outdoor air requirements, kitchen exhaust, heat removal and refrigeration equipment Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SHOPPING CENTER SYSTEM DESIGN
Regional shopping centers vary widely in physical arrangement and architectural design. Single level and smaller centers usually use unitary systems for mall and tenant air conditioning, multilevel and larger centers usually use a central system. The owner sets the design of the mall and generally requires that similar systems to be installed for tenant stores. A typical central system may distribute chilled water to individual tenant stores and to the mall air conditioning system. Central plant systems typically provide imporved efficiency and better overall economics of operation. Central systems may also provide the basic components required for smoke removal. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities SHOPPING CENTER AIR DISTRIBUTION
Air distribution in individual stores should be designed for the particular space occupancy. Some tenant stores maintain negative pressure relative to atmospheric pressure and a neutral pressure relative between most of the individual tenant stores. Exterior entrances should have vestibules or air curtains. Smoke management is required by many building codes, so air distribution should be designed to easily accommodate smoke control requirements. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities MULTIPLE-USE COMPLEXES
Multiple-use complexes are being developed in many metropolitan areas. These complexes generally combined retail facilities with other facilities such as offices, hotels, residences, or other commercial space into a single site. This consolidation of facilities into a single site or structure provides benefits such as improved land use, structural savings, more efficient parking, utility savings, and opportunities for more efficient electrical, fire protection and mechanical systems. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities MULTIPLE-USE COMPLEXES LOAD DETERMINATION
The various occupancies may have peak HVAC demand that occurs at different times of the day or year. Therefore, the HVAC loads of these occupancies should be determined independently. Where a combined central plant is considered, a block load should also be determined. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities MULTIPLE-USE COMPLEXES DESIGN CONSIDERATIONS
Retail facilities are generally located on the lower levels of multiple-use complexes, and other commercial facilities are on upper levels. Generally, the parameter loads of the retail portion differ from those of the other commercial spaces. Greater lighting and population densities also make HVAC demands for the retail space different from those for the other commercial space. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities MULTIPLE-USE COMPLEXES DESIGN CONSIDERATIONS
Retail facilities are generally located on the lower levels of multiple-use complexes, and other commercial facilities are on upper levels. Generally, the parameter loads of the retail portion differ from those of the other commercial spaces. Greater lighting and population densities also make HVAC demands for the retail space different from those for the other commercial space. The differences in HVAC characteristics for various occupancies within a multiple-use complex indicate that separate air handling and distribution should be used for the separate space. However, combining the cooling requirements of various facilities into a central plant can achieve a substantial saving. A combined central cooling plant for a multiple use complex also provides good opportunites for heat recovery, thermal storage and other similar functions that may not be economical in a single use facility. Engr. Fahad Hasan, Y.H.Associates,

Retail Facilities MULTIPLE-USE COMPLEXES SYSTEM DESIGN CONTROLS
Individual air handling and distribution system should be designed for the various occupancies. The central cooling plant may be sized for the block load requirements, which may be less than the sum of each occupancy’s demand. CONTROLS Multiple use complexes typically require centralized control. It may be dictated by requirements for fire and smoke control, security, remote monitoring, billing for central facilities use, maintenance control, building operations control and energy management. Engr. Fahad Hasan, Y.H.Associates,

Commercial and Public Buildings
Office building General Design Considerations Despite cyclical market fluctuations, office buildings are considered the most complex and competitive segments of real estate development. Sizes and Flexibility Office buildings are typically grouped into three categories. High rise (16 stories and above), mid rise (4 to 15 stories) and low rise (one to three stories) Floorplate (Floor Space Area) Size typically ranges from 18,000 to 30,000 sqft and averages from 20,000 to 25,000 sqft. Use and Ownership Office buildings can be single tenant or multitenant. A single tenant building can be owned by the tenant or leased from a landlord. From HVACR systems standpoint, a single tenant/owner is more cautious considering issues such as life cycle cost and energy conservations. In many cases systems are not selected based on the lowest first cost but life cycle cost. Engr. Fahad Hasan, Y.H.Associates,

Office building Load Characteristics Office buildings usually include both peripheral and interior zone spaces. The peripheral zone extends 10 to 12 ft inwards from the outer wall towards the interior of the building and frequently has large window area. These zones may be extensively subdivided. Peripheral zones have variable loads because of changing sun position and weather. Most office buildings are occupied from approximately 8:00 AM to 6:00 PM, many are occupied by some staff from as early as 5:30 AM to as late as 7:00 PM. Some tenants operations may require night work schedules, usually not beyond 10:00 PM. Office buildings may contain printing facilities, information and computing centers, or broadcasting studios, which could operate 24 hours a day. Therefore, for economical air conditioning design, the intended uses of an office building must be well established before design development. Engr. Fahad Hasan, Y.H.Associates,

Office building Load Characteristics Occupancy varies considerably. In accounting or other sections where clerical work is done, the maximum density is approximately one person per 75 sqft of floor area. Where there are private offices, the density may be as little as one person per 200 sqft. The most serious cases, however, are the occasional waiting rooms, conference rooms where occupancy may be as high as one person per 20 sqft The lighting load in an office building can be a significant part of the total heat load. Lighting and normal equipment electrical loads average from 1 to 5 watts/sqft but may be considerably higher, depending on the type of lighting and amount of equipment. Building with higher number of computer systems and other electronic equipment can have electrical loads as high as 5 watts/sqft to 10 watts/sqft. The amount, size and type of computer equipment anticipated for the life of the building should be accurately apprised to size the air handling equipment properly and provide for future installation of air conditioning apparatus. Engr. Fahad Hasan, Y.H.Associates,

Office building Load Characteristics Total lighting heat output from recessed fixtures can be withdrawn by exhaust or return air and thus kept out of space conditioning supply air requirements. By connecting a duct to each fixture, the most balanced air system can be provided. However, this method is expensive, so the suspended ceiling is often used as a return air plenum with air drawn from the space to above the suspended ceiling. Building shape and orientation are often determined by the building site, but some variations in these factors can increase refrigeration load. Shape and orientation should therefore be carefully analyzed in the early design stages. Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept The variety of functions and range of design criteria applicable to office buildings have allowed the use of almost every available air conditioning system. Multistory structures are discussed here, but the principles are criteria are similar for all sizes and shapes of office buildings. Attention to detail is extremely important, especially in modular buildings. Each piece of equipment, duct and pipe connections and the like may be duplicated hundreds of times. Thus, seemingly minor design variations may substantially affect construction and operation costs. In initial design, each component must be analyzed not only as an entity, but also as part of an integrated system. This system design approach is essential for achieving optimum results. Built-in system flexibility is essential for office building design. Business office procedures are constantly being revised, and basic building services should be able to meet changing tenant needs. Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept The type of occupancy may have an important bearing on air destruction system selection. For buildings with one owner or lessee, operations may be defined clearly enough that a system can be designed without the degree of flexibility needed for a less well defined operation. However, owner occupied buildings may require considerable design flexibility because the owner will pay for all alterations. The speculative builder can generally charge alterations to tenants. When different tenants occupy different floors or even parts of the same floor, the degree of design and operation complexity increases to ensure proper environmental comfort conditions to any tenant, group of tenants or all tenants at once. This problem is more acute if tenants have seasonal and variable overtime schedules. Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept Certain areas may have hours of occupancy or design criteria that differ substantially from those of the office administration areas, such areas should have their own air distribution systems and in some cases, their own refrigeration equipment. Main entrances and lobbies are sometimes served by a separate and self contained system because they buffer the outdoor atmosphere and the building interior. Some engineers prefer to have a lobby summer temperature 4 to 6 deg F above office temperature to reduce operating cost and temperature shock to people entering or leaving the building. Incase where lobbies or main entrances have longer or constant operation, a dedicated/ self contained HVAC system is recommended to allow turning off other building systems Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept The unique temperature and humidity requirements of server rooms or computer data processing installations, and the fact that they often run 24 hours per day for extended periods, generally warrant separate refrigeration and air distribution systems. Separate back up systems may be required for data processing areas in case the main building HVAC system fails. The degree of air filtration required should be determined. Service cost and effect of air resistance on energy cost should be analyzed for various types of filters. Initial filter cost and air pollution characteristics also need to be considered. Activated charcoal filters for odor control and reduction of outdoor air requirements are another option to consider. Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept Providing office buildings with continuous 100% outdoor air is seldom justified, so most office buildings are designed to minimize outdoor air use, except during economizer operation. However, attention to indoor air quality may dictate higher levels of ventilation air. In addition, the minimum volume of outdoor air should be maintained in variable volume air handling systems. Suspended ceiling return air plenums eliminate sheet metal return air ductwork to reduce floor to floor height requirements. However, suspended ceiling plenums may increase the difficulty of proper air balancing throughout the building. Problems often connected with suspended ceiling return plenum includes: Air leakage through cracks, with resulting fungus tendency of return air openings nearest to a shaft opening or collector duct to pull too much air, thus creating uneven air motion and possible noise Noise transmission between office spaces . Engr. Fahad Hasan, Y.H.Associates,

Office building Design Concept Air leakages can be minimized by proper workmanship. To overcome drawing too much air, return air ducts can be run in the suspended ceiling pathway from the shaft, often in a simple radical pattern. Ends of ducts can be left open or dampered. Generous sizing of return air grilles and passages lowers the percentage of circuit resistance attributable to the return air path. This bolsters effectiveness of supply air balancing devices and reduces the significance of air leakage and drawing too much air. Structural blockage can be solved by locating openings in beams or partitions with fire dampers, where required. Engr. Fahad Hasan, Y.H.Associates,

Airport Airports are large, complex enterprises usually run directly by government entities or by government created authorities. Airport typically consists the following: Runways and taxiing areas Air traffic control building Aircraft maintenance buildings and hangers Passenger terminals and car parking (open, partially open, totally enclosed) Freight warehouse Lodging facilities (hotels) Inaddition, support areas such as administration buildings, central utility plants, and transit facilities (rail and/or bus) are common in airport facilities Engr. Fahad Hasan, Y.H.Associates,

Airport Load Characteristics Terminal buildings consist of large, open circulating areas, one or more floors high, often with high ceilings, ticketing facilities. Lighting and equipment loads are generally average but occupancy varies substantially. Exterior loads are of course a fraction of architectural design. The largest single problem often is thermal drafts created by large entrance ways, high ceilings, and long passageways that have openings to the outdoors. Engr. Fahad Hasan, Y.H.Associates,

Airport Design Considerations Airports are generally consist of one or more central terminal buildings connected by long passageways or trains to rotundas containing departure lounges for airplane loading. Most terminals have portable telescoping type loading bridges connecting departure lounges to the airplanes. These passageways eliminate heating and cooling problems associated with traditional permanent passenger loading structures. Because of difficulties in controlling the air balancing and because of the many outdoor openings, high ceilings, and long, low passageways (which often are not air conditioned), the terminal building (usually air conditioned) should be designed to maintain a substantial positive pressure. Zoning is generally required in passenger waiting areas, in departure lounges, and at ticket counters to take care of the widely variable occupancy loads. Engr. Fahad Hasan, Y.H.Associates,

HVAC DESIGN CONSIDERATIONS

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